The Great Blue Hole, a submarine sinkhole off the coast of mainland Belize, yawns wide in an image captured by GeoEye's Ikonos satellite on Dec. 8.

The Great Blue Hole is one of the natural wonders of the world, lying off the coast of Belize in the midst of the Lighthouse Reef Atoll. It's a circular sinkhole measuring about 1,000 feet (300 meters) wide and more than 400 feet (124 meters) deep. It was apparently formed as part of a cave system tens of thousands of years ago, when sea levels were much lower. When the ocean's waters rose, the caves were flooded. The Great Blue Hole is part of the Belize Barrier Reef Reserve System, which UNESCO has designated a World Heritage Site.

Archaeologists and historians say the reef system provided fishing grounds for Maya communities more than a millennium ago, and later served as a haven for 17th-century pirates and buccaneers. Today, the reef is a haven for scuba divers and for marine species at risk, including West Indian manatees and green turtles.

This picture of the sinkhole and its surroundings was captured by GeoEye's Ikonos satellite on Dec. 8, from an altitude of 423 miles (681 kilometers).